This invention relates to fibre-optic cable assemblies.
Where fibre-optic cables are used in environments subjected to repeated, large changes in temperature, the optical fibre can become damaged as a result of differential thermal expansion effects in the cable. The optical fibre is often made from a silica material which has a low coefficient of thermal expansion. The problem with this is that the sheath within which the fibre extends is of a different material with a markedly different coefficient of expansion. Where the sheath is of a glass fibre, this has a relatively high positive temperature coefficient whereas a sheath made of an aramid such as Kevlar may have a negative coefficient of expansion. Where both the fibre and the sheath are fixed in terminations at both ends, it can be seen that this will result in a force on the fibre. Depending on the way in which the cable is terminated and on whether the temperature is increasing or decreasing, this force could result in movement of the fibre within the termination or cause fatigue, as a result of repeated compressive or tensile forces. Movement of the fibre is undesirable because it can lead to inefficiency in optical coupling; it can also lead to damage of the fibre. Stress of a fibre which is fixed immovably within a termination can lead to fracture or change in the optical properties of the fibre.